This study aimed to find out how and on what level the students of two separate secondary schools shared and constructed knowledge on imperialism by interacting through historical role characters in a Web-based environment. Furthermore, the study aimed to find out how social and contextual features affected the nature of knowledge sharing and construction. The data about the history project were gathered by various means in order to validate the findings of the case study. The results demonstrated that the level of the Web-based messages remained quite low. Also the use of the Web-based environment in terms of shared knowledge construction was rather weak. In comparison, different instructional activities of the two teachers resulted in different learning activities in the two schools and, thus, different level of interaction in the Web-based environment. The findings of this research are discussed in terms of important factors influencing the knowledge sharing and constructing activities. Forms of Co-Operation in Dyadic Problem Solving is appended. (Contains 2 tables.)